The long term focus of this research is the regulation of cell division in the male germline and the coordination of the cell cycle with spermatocyte development and differentiation. In Drosophila, molecular genetic analyses have identified the boule gene as a key regulatory of meiosis in males. Spermatogenesis in boule mutants is normal up to meiosis, but the G2/M transition of meiosis I fails to occur and males are sterile. Molecular studies have revealed that boule belongs to a conserved family of fertility factors that includes the Daz (Deleted in Azoospermia) gene, a candidate locus for the human Azoospermia Factor (AZF). Whereas the molecular role of its vertebrate homologs in spermatogenesis has not been defined, Boule has been shown to be essential for translation of the cdc25 phosphatase Twine, a key component of the cell cycle machinery. The four specific aims of this proposal are directed at identifying the targets, functional domains, pairing partners, and regulators of the Boule protein. A transgenic approach will be used to analyze the function of Boule, an RNA-binding protein, in Twine regulation. Deletion derivatives and site-directed points mutants will be employed to analyze Boule structure and function both in vitro and in vivo. A yeast two-hybrid screen will be carried out to identify proteins that interact directly with the Boule protein. Lastly, a collection of male-sterile mutants will be screened for regulators for Boule expression and activity. These studies should provide insight into the basic regulatory mechanisms governing cell division in gametogenesis, as well as be of substantial relevance to the investigation and treatment of a significant genetic cause of infertility in men.